PRESSURE BOMB COMPARISON ACROSS ALL FIELDS
The above figure for 2020 shows that the non-saline Eastside and Westside fields are closer than they were for 2019 until the end of August. At this time the non-saline east field is showing the greatest stress at -14 bars. This field has been deficit irrigated due to infiltration and disease issues, receiving about 4 inches less water than the other fields since May. I can't say why, but from 7/23 – 8/31, the SWP for the MidSalt and HiSalt sites showed the same non-stressed value of -12 bars. The additional osmotic stress from the hi-salt area should cause an SWP that is at about -2 bars more stress than the mid-salt area and non-saline eastside and westside. Good irrigation scheduling and high-frequency pulsed irrigation are helping this saline field.
NON-SALINE EASTSIDE FIELD
The green to red image on the left indicates the volume and vigor of the canopy foliage as a Normalized Differential Vegetative Index (NDVI). The right image shows the relative water stress across the orchard as calculated using the infrared canopy temperature. The Demo monitoring is mostly for the western 80 acres in this image and an average SWP of about -14 bars makes sense with the half blue and green shown in this CERES water stress canopy temperature image. However, we have a -21 bar SWP in the NE field and mostly yellow and red in the CERES image, which indicates stress. I could see a bit more stress looking at the trees from the ground, but this field was irrigated with almost exactly the same amount of water as the other fields in this image. As of 8/31 stored soil moisture had dropped only 5% from the end of July according to the Jain Logic probe (see below), but a “hand-feel” moisture estimate using a Lord-type soil probe to 3 feet showed a 25% drop in available moisture.
TREE STRESS: Using the tree as the continuous integrated moisture sensor is somewhat possible using a dendrometer that measures the real-time daily shrink/swell and growth of the tree. The Phytech company is helping us do that by generating this average growth information in the below figure over three trees instrumented with dendrometers:
This is exactly the pattern that you want to see, up to mid-July – steadily increasing growth running 15-30 microns/day over the spring and early summer. From Mid-June to July 17 these trees averaged 6000 microns (6 mm) additional radial growth. That's a 12 mm, or almost ½ inch increase in trunk diameter. The blue bars indicate the timing and duration of irrigation of this high frequency double-line drip system. But from the end of July there is very little growth – probably due to the carbohydrate demand from the filling nuts. You would still like to see a little more growth than shown but the good news is that the daily shrink/swell (shown by the daily high and low in the chart and numbers at the bottom) is in the non-stressed range of 30-40 microns.
So what about the -21 bar SWP stress we measured on the NE block? We are fortunate to have 3 dendrometers on this block also which show a similar steady growth increase through July, as we did with the west 80 acres, but the slope is a little less and erratic compared to the west 80 acres. Then from July- August there is slight to no growth but the daily shrink/swell is still in the 25-40 micron range that indicates minimal stress.
The ROOTZONE SUM chart below from the Jain Logic monitoring system using a Sentek Drill & Drop capacitance probe that measures soil moisture to a depth of 46 inches shows that the total root zone soil moisture has fallen off about 15% during harvest cuttoff. The numbers on the left access are the sum of the percent soil moisture measured by each sensor placed every 4 inches. If these numbers were absolutely accurate, it would mean that this Nord Series fine sandy loam soil would hold 42% water (5.0”/ft) at field capacity, which is impossibly high. The correct number is about 28%, 3.4 inches/foot (about 2” available) as measured by a neutron probe. But the good news is that the trends in increased and decreased water content are very real and dependable. So the infiltration chart (top left) is an accurate indicator of how deep water penetrates (dark blue columns) every irrigation. This shows that the water only went to 26” over the last month, so there is no deep percolation lost below the root zone.
NON-SALINE WESTSIDE FIELD
AERIAL IMAGERY: There is definitely more blue in this image compared to the Eastside CERES image. At the end of July this grower finished connecting a new filter station for this field to canal water and then had the capacity to run the whole 300 acres in one set. This increased on-time allowed him to maintain reserve soil moisture and actually decrease tree stress (As shown with the pressure bomb SWP numbers in white.) during August compared to the Eastside non-saline field – even though this Pleasant Valley Westside field has a higher ET demand and much larger crop. To achieve this goal, this means that the Westside grower has applied 38” of water according to our flowmeters compared to 28” of water applied to the Eastside block.
TREE STRESS: Unfortunately, web connectivity and other problems have meant that only a little of the Phytech dendrometer data came through. There were 4 days data in June showing as good of growth as the best Eastside block but a higher amount of daily shrink/swell (MDS) of the trunk. This indicates that the tree has more stress on it moving the water up from the soil and out the leaf to meet ET during the day. The below 4 day snapshot shows less MDS (less stress) than June but no growth—probably because of the 6,000 +lb/ac crop on the trees.
SOIL MOISTURE: We have two sites in this field with instrumentation. The NO COVER site below is 80 rows east of the west edge of the field with the soil classed as a Cerrini sandy loam. The soil at this site is sandier than the Eastside field. The irrigation system is a single-line drip with four 1 gallon/hr drippers per tree. Irrigation was typically a 24 hr set every other day starting in June. With the new filter station on-line the grower ran two 72 hour sets back to back the third week of July. The Root Zone Sum chart shows a consistent water content refill after each irrigation. The Infiltration chart (top left) shows only a couple irrigations penetrated to 46” at this sandy loam site.
The COVER crop site (below) is 30 rows from the eastern edge of the field and is a Calflax clay loam with a definitely higher water holding capacity than the Cerrini SL in the NO_COVER area. This location and the NO_COVER location are in the same irrigation set, receiving water at the same time and duration – typically 24 hours. But with a heavier soil, this site is showing water infiltrating nearly every irrigation as opposed to the sandy loam area just 50 rows to the east. There is possibly a crack adjacent to a dripper that connects with the Sentek probe and pipes water down the side. From 7/24-8/22 the grower fired up a second filter station connected to canal water to irrigate the entire field (designed as a two set system) at one time – running for 6 days straight, off one day and then back on (as you can see in the infiltration chart top left). Despite this increased irrigation the Jain Logic/Sentek probe still shows about a 10% loss of stored moisture from June. But somehow the increased frequency and possibly the high quality canal water (only 30% of the salt of the groundwater) reduced the SWP stress on the trees. Of all the sites to have a failure in the Phytech dendrometers, this is possibly the worst one. Calculated flowrate for this 17x19 foot spacing with 4, 1 gph netafim button emitters/tree = 0.48 inches/day.
SEMI-SALINE, SALINE LEMOORE FIELD
AERIAL IMAGERY: As expected, the significant variability in canopy growth caused by excess salt and poor soil structure in this field produces the lowest and most variable Normalized Differential Vegetative Index (NDVI, left) and usually more WATER STRESS than in any other field. Should more leaching have been done during the winter to further reduce root zone salt loads? Perhaps the grower could have done more, but he applied 10 inches during the winter, which takes forever to penetrate in this saline-sodic Lethent silty clay loam, and his June 2020 SWP was less negative than June 2019 and now the July and August 2019 SWP shows even less stress than June. This is a square quarter-section field with a double-line high frequency automated drip system with two ¼ mile hose runs, running in 3 to 8 hour sets. There is a distinct stress pattern along the hose ends in the center and N and S borders of this field very similar to what we saw in the non-saline westside field with similar lengths of hose run. These are all pressure compensated drip emitters and any time I have checked the pressure at the hose end it is >12 psi which should be sufficient for max flow. So I'm guessing more emitters just get clogged and don't clean out during flushing. Maybe it would help to increase filter station/booster pressure and flush hoses more often. The grower used to run longer sets but that exacerbated the waterlogging problem.
TREE STRESS, SEMI-SALINE: Even though there is definite canopy size, ET and yield reduction in the best semi-saline area of this block compared to our non-saline fields, there was still excellent growth recorded by the Phytech dendrometers from May to July. In fact, the three trees with dendrometers in the NE area (D05) of this block put on an average 10,000 microns (10 mm) additional radial growth. That's a 20 mm, or ¾ inch increase in trunk diameter – the highest growth rate of all our monitoring sites even with extra stress from the salt! Must be the seaweed extract this grower uses, hmmm. That growth has stopped for August as all the energy is going to fill nuts, but the MDS is 30-40% less than the saline area – close to the MDS of the other non-saline fields.
TREE STRESS, SALINE: This severely affected saline area in the south central part of the block surprised us last year with about half the growth of the Semi-saline Area. Nevertheless, this year it has had essentially ZERO growth all season and even shows slight shrinkage for this July-August. The maximum daily shrink/swell (MDS) change over 24 hours is also the largest of any site – measuring about 60-70 microns.
SEMI-SALINE: The second highest total Root Zone Summed water content is this area – reflecting a soil texture finer than any of the non-saline problem fields and very slow drainage through the profile. The deepest penetration during an irrigation for August is only 12”. The impact of anoxia, waterlogging, has just as much negative impact on pistachio growth as does the higher salinity. Still, the trees need the water and this grower has increased the frequency of 3 hour pulsed irrigation, which hopefully still allows time for some reoxygenation of the rootzone.
SOIL MOISTURE, SALINE: The highest total Root Zone Summed water content is in this area (D03) of the field. Frequently prone to ponding many trees have died here. The deepest recorded irrigation penetration for any 3 to 8 hour event is 14”. Installing an automated WiseCon irrigation system to run very short sets as often as daily has been the best strategy the grower found to reduce anaerobic conditions in the root zone and improve tree growth. You can see that irrigation was cutoff for harvest on 9/4.